Text.PrettyPrint bug or doc bug
Hello, The documentation for Text.PrettyPrint.HughesPJ states that vcat is the "List version of $$", but it works as the list version ($+$). In the source code, this is because vcat = reduceAB . foldr (above_' True) empty instead of vcat = reduceAB . foldr (above_' False) empty So either the documentation needs to be changed or the code. It would be nice to have both versions. Cheers, - Marcus
On Wed, Feb 24, 2010 at 01:10:38PM +0100, Marcus D. Gabriel wrote:
The documentation for Text.PrettyPrint.HughesPJ states that vcat is the "List version of $$", but it works as the list version ($+$).
So either the documentation needs to be changed or the code. It would be nice to have both versions.
It looks like the behaviour changed in Tue Jun 24 12:37:15 BST 2008 benedikt.huber@gmail.com * fillNB bug, lazy vcat i.e. the version that came with GHC 6.10. As it's had the current behaviour for some time, it would probably make sense to have a library submission to determine what the behaviour should be, and whether we want another function for the other behaviour: http://www.haskell.org/haskellwiki/Library_submissions Thanks Ian
Ian Lynagh schrieb:
On Wed, Feb 24, 2010 at 01:10:38PM +0100, Marcus D. Gabriel wrote:
The documentation for Text.PrettyPrint.HughesPJ states that vcat is the "List version of $$", but it works as the list version ($+$).
So either the documentation needs to be changed or the code. It would be nice to have both versions.
Hi, do you have a actual use case for the "List version of $$" ? It would make a good test I suppose.
It looks like the behaviour changed in
Tue Jun 24 12:37:15 BST 2008 benedikt.huber@gmail.com * fillNB bug, lazy vcat
i.e. the version that came with GHC 6.10. As it's had the current behaviour for some time, it would probably make sense to have a library submission to determine what the behaviour should be, and whether we want another function for the other behaviour: http://www.haskell.org/haskellwiki/Library_submissions
This is indeed a bug; I've reported it back in December 2008, but unfortunately did not file a bug report: http://www.haskell.org/pipermail/libraries/2008-December/011032.html (at the end of the message, starting with [1]) Personally I think the "List version of $+$" is more common, but changing the implementation seems also fine. It would be nice to solve the other (trickier) issue discussed in the mail referenced above as well. cheers, benedikt
No, I do not really have a use case. I discovered it upon recompiling an older program whereupon the pretty printing behaviour changed which is how I discovered the inconsistency between the code and the documentation. Essentially, I just wanted to make columns, one line at a time. So, -- dwiw == do what i (basically) want dwiw :: [Doc] -> Doc dwiw = foldr ($$) empty f2 :: ([Doc] -> Doc) -> IO () f1 = \f -> (putStrLn $ render $ f [nest 0$text "abc", nest 10$text "def", nest 20$text "hig"]) f2 :: ([Doc] -> Doc) -> IO () f2 = \f -> (putStrLn $ render $ f [nest 0$text "abc", nest 10$text "def4567890123456789", nest 20$text "hig"]) *> mapM_ f1 [vcat,dwiw] abc def hig abc def hig *> mapM_ f1 [vcat,dwiw] abc def4567890123456789 hig abc def4567890123456789 hig Does that make visual sense? The logic is as follows: 1/ Figure out the size of your columns in advance to use nest; 2/ Require that the sum of the columns sizes is less than or equal to the maximum length of line that you are willing to tolerate; and 3/ dwiw splits the line if and when needed. Cheers, - Marcus P.S. I missed your previous post Ian; thanks for it. Benedikt Huber wrote:
Ian Lynagh schrieb:
On Wed, Feb 24, 2010 at 01:10:38PM +0100, Marcus D. Gabriel wrote:
The documentation for Text.PrettyPrint.HughesPJ states that vcat is the "List version of $$", but it works as the list version ($+$).
So either the documentation needs to be changed or the code. It would be nice to have both versions.
Hi, do you have a actual use case for the "List version of $$" ? It would make a good test I suppose.
It looks like the behaviour changed in
Tue Jun 24 12:37:15 BST 2008 benedikt.huber@gmail.com * fillNB bug, lazy vcat
i.e. the version that came with GHC 6.10. As it's had the current behaviour for some time, it would probably make sense to have a library submission to determine what the behaviour should be, and whether we want another function for the other behaviour: http://www.haskell.org/haskellwiki/Library_submissions
This is indeed a bug; I've reported it back in December 2008, but unfortunately did not file a bug report:
http://www.haskell.org/pipermail/libraries/2008-December/011032.html (at the end of the message, starting with [1])
Personally I think the "List version of $+$" is more common, but changing the implementation seems also fine.
It would be nice to solve the other (trickier) issue discussed in the mail referenced above as well.
cheers, benedikt
Hi, I filed a bug (http://hackage.haskell.org/trac/ghc/ticket/3911) referencing this discussion, and attached a patch fixing the problem. On 02.03.2010, at 09:44, Marcus D. Gabriel wrote:
No, I do not really have a use case. I discovered it upon recompiling an older program whereupon the pretty printing behaviour changed which is how I discovered the inconsistency between the code and the documentation. Oh, this seems like a reasonable use/test case, thank you.
cheers, benedikt
Essentially, I just wanted to make columns, one line at a time. So,
-- dwiw == do what i (basically) want dwiw :: [Doc] -> Doc dwiw = foldr ($$) empty
f2 :: ([Doc] -> Doc) -> IO () f1 = \f -> (putStrLn $ render $ f [nest 0$text "abc", nest 10$text "def", nest 20$text "hig"])
f2 :: ([Doc] -> Doc) -> IO () f2 = \f -> (putStrLn $ render $ f [nest 0$text "abc", nest 10$text "def4567890123456789", nest 20$text "hig"])
*> mapM_ f1 [vcat,dwiw] abc def hig abc def hig *> mapM_ f1 [vcat,dwiw] abc def4567890123456789 hig abc def4567890123456789 hig
Does that make visual sense?
The logic is as follows: 1/ Figure out the size of your columns in advance to use nest; 2/ Require that the sum of the columns sizes is less than or equal to the maximum length of line that you are willing to tolerate; and 3/ dwiw splits the line if and when needed.
Cheers, - Marcus
P.S. I missed your previous post Ian; thanks for it.
Benedikt Huber wrote:
Ian Lynagh schrieb:
On Wed, Feb 24, 2010 at 01:10:38PM +0100, Marcus D. Gabriel wrote:
The documentation for Text.PrettyPrint.HughesPJ states that vcat is the "List version of $$", but it works as the list version ($+$).
So either the documentation needs to be changed or the code. It would be nice to have both versions.
Hi, do you have a actual use case for the "List version of $$" ? It would make a good test I suppose.
It looks like the behaviour changed in
Tue Jun 24 12:37:15 BST 2008 benedikt.huber@gmail.com * fillNB bug, lazy vcat
i.e. the version that came with GHC 6.10. As it's had the current behaviour for some time, it would probably make sense to have a library submission to determine what the behaviour should be, and whether we want another function for the other behaviour: http://www.haskell.org/haskellwiki/Library_submissions
This is indeed a bug; I've reported it back in December 2008, but unfortunately did not file a bug report:
http://www.haskell.org/pipermail/libraries/2008-December/011032.html (at the end of the message, starting with [1])
Personally I think the "List version of $+$" is more common, but changing the implementation seems also fine.
It would be nice to solve the other (trickier) issue discussed in the mail referenced above as well.
cheers, benedikt
participants (3)
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Benedikt Huber -
Ian Lynagh -
Marcus D. Gabriel